L0301P2 - Biology of Cells
Histology *study of micro-anatomy - microscopic structure of tissues Cell Types in the Adult Human *cells have remarkable variation: **in cell structure, cell function, cell gene expression *different structure due to different function *determined by abundance and proportion of: **metabolically active organelles **metabolically inactive inclusions **cytoplasmic matrix - structurally undifferentiated The Eukaryotic Cell *compared to prokaryotic cells **distinct nucleus containing DNA **histones associated with DNA **numerous membrane-bound organelles in the cytoplasm: ***rough/smooth ER ***golgi complex ***mitochondria, etc. Nucleus *composed of: **nuclear envelope (which have nuclear pores) **chromatin **nucleolus **nuclear matrix Number of Nuclei *mature erythrocytes - 0 nucleus *most cells in the body - 1 nucleus *cardiac muscle cells - 2 nuclei *osteoclast - macrophage of bone - up to 50 nuclei per cell *skeletal muscle cell - 10,000s of nuclei Plasma Membrane *asymmetrical, dynamic, fluid structure **some proteins move around the membrane but very little movement across monolayers (flip flop) Function *highly selective filter *generates difference in ion concentrations *sensor of external signals Comprises *lipids - constitutes ~50% mass **phospholipid bilayer ***hydrophilic head ***2 hydrophobic tails ***in water - spontaneously aggregate to form micelles of bilayers **cholesterol ***nearly one for every phospholipid ***decreases permeability of lipid bilayers to small-water molecules **glycolipids ***only found in outer half the bilayer ***functions are largely unknown *proteins **transport, enzymes, provides links, receptors **most extend across the lipid bilayer ***have three domains: intracellular, transmembrane, extracellular *carbohydrates **located exclusively on the outside surface of all eukaryotic cells **roles in cell-cell and cell-matrix recognition Mitochondrion *present in all eukaryotic cells Structure *spherical and filamentous *two membranes: inner (with cristae) and outer *two spaces: intramembranous (intracristal), intercristal *cristae **increase surface are of the inner mitochondrial membrane *matrix **rich in proteins and contains DNA, RNA, electron-dense granules rich in calcium and magnesium and enzymes for Krebs cycle and fatty acid oxidation Function *transfer energy in metabolites into energy that is accessible to the cell (ATP) Ribosomes *extremely small - not possible to see a single ribosome *composed of rRNA and ~80 proteins *involved in translation (protein synthesis) *found in all cells (prokaryotes and eukaryotes) **free in the cytosol - where proteins destined to be used within the cell are produced **on RER - where proteins to be secreted are produced *can occur individually or in clusters (polysomes/polyribosomes) Rough Endoplasmic Reticulum *a.k.a Granular ER, RER *membrane network + ribosomes *involved in synthesis and secretion of proteins that are to be: **included in specific membranes **stored in granules **secreted *newly synthesised protein accumulates in the lumen (empty space) of the RER - then transported to the golgi apparatus *prominent in cells specialised for protein secretion Smooth Endoplasmic Reticulum *a.k.a SER *no ribosomes *involved in steroid synthesis, breakdown of glycogen, detoxification of hormones and drugs *sarcoplasmic reticula of muscle cells are a specialised form of SER which are involved in calcium release Golgi Apparatus/Complex *chemically modifies, sorts and packages proteins for secretion *consists of ~3-5 flattened membranous sacs - cisternae *almost always has a curved structure *last membranous sac before the vesicle is secreted is called the mature face Constitutive Secretion *immediate secretion after budding off from golgi complex Regulated Secretion *protein is stored in a granule in a vesicle and only released when instructed to Lysosomes *present in nearly all cells *abundant in phagocytic cells *membrane-bound vesicles that contain a range of hydrolytic enzymes: **acid phosphates **proteases **ribonucleases **lipases Function *intracytoplasmic digestion *three stages of digestion: **primary - not yet entered into a digestive event - are homogenous in appearance **secondary - digestion is occurring - are heterogenous in appearance **residual bodies - vacuoles containing indigestible materials Granules *store products in cells **enzymes in stomach cells **histamine in mast cells *sit in the cell surrounded by a membrane *contain concentrated form of secretory product ** ~200 times the concentration in the rough ER Cytoskeleton Important Role *maintaining shape of cells *cell migration *cell movement (including contraction) *movement of parts of cells eg. cilia *movement of organelles within the cell *certain specialised cell functions eg. mitotic spindle Microfilaments *made of: **actin ***abundant in most cells ***globular molecules arrange in a double helix ***important for cell motility **myosin ***low abundance in most cells, except muscle (high abundance) Microtubules *straight cylindrical tubules (hollow) *13 parallel protofilaments composed of dimers *constantly assembled and disassembled *functions: **maintenance of cell shape **movement of organelles within the cell **movement of cilia and flagella Intermediate Filaments *a family of structurally similar, but chemically distinct filaments *includes: **keratins - epithelia **vimentin - mesenchymal cells and derivatives **desmin - muscle cells **glial fibrillary acidic proteins - astrocytes